The present invention relates generally to providing network services such as load balancing, packet filtering, or Network Address Translation (NAT). Network services are provided using service managers that synchronize instructions that are carried out using a distributed network of forwarding agents.
As the IP protocol has continued to be in widespread use, a plethora of network service appliances have evolved for the purpose of providing certain network services not included in the protocol and therefore not provided by standard IP routers. Such services include NAT, statistics gathering, load balancing, proxying, intrusion detection, and numerous other security services. In general, such service appliances must be inserted in a network at a physical location where the appliance will intercept all flows of interest for the purpose of making its service available.
FIG. 1 is a block diagram illustrating a prior art system for providing a network service. A group of clients 101, 102, and 103 are connected by a network 110 to a group of servers 121, 122, 123, and 124. A network service appliance 130 is physically located in the path between the clients and the servers. Network service appliance 130 provides a service by filtering packets, sending packets to specific destinations, or, in some cases, modifying the contents of packets. An example of such modification would be modifying the packet header by changing the source or destination IP address and the source or destination port number.
Network service appliance 130 provides a network service such as load balancing, caching, or security services. In providing security services, network service appliance 130 may function as a proxy, a firewall, or an intrusion detection device. For purposes of this specification, a network service appliance that acts as a load balancer will be described in detail. It should be noted that the architecture and methods described are equally applicable to a network service appliance that is functioning as one of the other above described devices.
Network service appliance 130 is physically located between the group of servers and the clients that they serve. There are several disadvantages to this arrangement. First, it is difficult to add additional network service appliances when the first network service appliance becomes overloaded because the physical connections of the network must be rerouted. Likewise, it is difficult to replace the network service appliance with a back up network service appliance when it fails. Since all packets pass through the network service appliance on the way to the servers, the failure of the network service appliance may prevent any packets from reaching the servers and any packets from being sent by the servers. Such a single point of failure is undesirable. Furthermore, as networks and internetworks have become increasingly complex, multiple services may be required for a single network and inserting a large number of network service appliances into a network in places where they can intercept all relevant packet flows may be impractical.
The servers may also be referred to as hosts and the group of servers may also be referred to as a cluster of hosts. If the group of servers has a common IP address, that IP address may be referred to as a virtual IP address (VIPA) or a cluster address. Also, it should be noted that the terms client and server are used herein in a general sense to refer to devices that generally request information or services (clients) and devices that generally provide services or information (servers). In each example given it should be noted that the roles of client and server may be reversed if desired for a particular application.
A system that addresses the scalability issues that are faced by network service appliances (load balancers, firewalls, etc.) is needed. It would be useful to distribute functions that are traditionally performed by a single network element and so that as much function as possible can be performed by multiple network elements. A method of coordinating work between the distributed functions with a minimum of overhead is needed.
Although network service appliances have facilitated the development of scalable server architectures, the problem of scaling network service appliances themselves and distributing their functionality across multiple platforms has been largely ignored. Network service appliances traditionally have been implemented on a single platform that must be physically located at a specific point in the network for its service to be provided.
For example, clustering of servers has been practiced in this manner. Clustering has achieved scalability for servers. Traditional multiprocessor systems have relatively low scalability limits due to contention for shared memory and I/O. Clustered machines, on the other hand, can scale farther in that the workload for any particular user is bound to a particular machine and far less sharing is needed. Clustering has also facilitated non-disruptive growth. When workloads grow beyond the capacity of a single machine, the traditional approach is to replace it with a larger machine or, if possible, add additional processors within the machine. In either case, this requires downtime for the entire machine. With clustering, machines can be added to the cluster without disrupting work that is executing on the other machines. When the new machine comes online, new work can start to migrate to that machine, thus reducing the load on the pre-existing machines.
Clustering has also provided load balancing among servers. Spreading users across multiple independent systems can result in wasted capacity on some systems while others are overloaded. By employing load balancing within a cluster of systems the users are spread to available systems based on the load on each system. Clustering also has been used to enable systems to be continuously available. Individual application instances or machines can fail (or be taken down for maintenance) without shutting down service to end-users. Users on the failed system reconnect and should not be aware that they are using an alternate image. Users on the other systems are completely unaffected except for the additional load caused by services provided to some portion of the users that were formerly on the failed system.
In order to take full advantage of these features, the network access must likewise be scalable and highly available. Network service appliances (load-balancing appliances being one such example) must be able to function without introducing their own scaling limitations that would restrict the throughput of the cluster. A new method of providing network services using a distributed architecture is needed to achieve this.
When network services are provided using a distributed architecture, the problem of synchronizing actions among the forwarding agents arises. Traditional two-phase commit protocols can be used, but such protocols are time consuming and also use considerable resources for the purpose of generating confirmations. This is especially problematic for a network that includes a number of routers or switches having forwarding agents and where each router or switch must synchronize service instructions with other devices. (It should be noted that for the purpose of brevity, routers will be referred to in examples hereinafter; it should be understood that a switch may also be used where appropriate.) Traditional two-phase commit schemes are too cumbersome and slow for the routing fabric. Since the routers are separate devices physically located remotely from each other, a scheme relying on a shared media used by the routers would be impractical. Each service manager would use resources to confirm every instruction to every router.
What is needed is a scheme for synchronizing instructions across multiple routers in the absence of shared media or two-phase commit protocols.
A scheme wherein a service manager is used as a point of synchronization and distribution of filters among routers is disclosed. Filters are used to determine how routers are to handle packets. Forwarding agents on the routers cache filters received from the service manager. Instructions are sent to the forwarding agents without reliance on a two phase commit scheme to confirm receipt of instructions. Instructions may be periodically resent on an as needed basis. In this robust scheme, forwarding agents consult the service manager whenever instructions are not found by the forwarding agent for handling packets controlled by the service manager. Forwarding agents only consult the service manager when necessary and the scheme does not require verified communication between the service manager and the forwarding agent.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication lines. Several inventive embodiments of the present invention are described below.
In one embodiment, a method of obtaining instructions for routing a packet includes receiving a packet having a packet flow identifier that includes a packet source IP address, a packet destination IP address, a packet source port, and a packet destination port and checking whether the packet flow identifier matches a stored instruction. If the packet flow identifier does not match a stored instruction, whether the packet flow identifier matches a stored criteria is checked and if the packet matches a stored criteria, the packet is forwarded to a service manager.
In another embodiment, a forwarding agent includes a packet receiving interface configured to receive a packet having a packet flow identifier that includes a packet source IP address, a packet destination IP address, a packet source port, and a packet destination port and a processor configured to check whether the packet flow identifier matches a stored instruction and if the packet flow identifier does not match a stored instruction, checking whether the packet flow identifier matches a stored criteria. A packet forwarding interface forwards the packet to a service manager if the packet matches a stored criteria.
In another embodiment, a network service manager includes a set up interface for specifying a set of packets for which the service manager will provide a network service and a forwarding agent communication interface on which packet interest instructions can be multicast to a plurality of forwarding agents for the purpose of instructing the plurality of forwarding agents to send certain packets in the set of packets to the service manager. On a packet receiving interface, the service manager can receive packets sent from a reporting forwarding agent in response to the multicast packet interest instructions. A processor processes the packet received on the packet receiving interface and determines an action for the reporting forwarding agent to take regarding the packet.
In another embodiment, a method of processing a packet at a router includes receiving a packet having packet flow identifier that includes a packet source IP address, a packet destination IP address, a packet source port, and a packet destination port and checking whether the packet flow identifier matches a general filter. Whether the packet flow identifier matches a specific filter is checked and if the packet flow identifier does not match the specific filter but does match the general filter the packet is sent to a service manager indicated by the general filter.
In another embodiment, a method of synchronizing packet handling instructions from a service manager to a router includes sending an interest filter to the router, the interest filter specifying a plurality of flows for which packets are to be sent to the service manager and receiving a requested packet corresponding to a specific one of the flows. Actions to be applied to the specific one of the flows are determined and an action filter is sent to the router that specifies an action to be performed for each packet in the specific one of the flows.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example the principles of the invention.